Improvement in A.C. dielectric breakdown strength of XLPE power cables through diffusing of an additive into the insulation

In order to halve the insulation thickness of extra-high-voltage XLPE power cables, verification of methods which improve the dielectric performance through the modification of the semiconducting layer is in progress. As part of these efforts, an additive which was found to be most effective by preliminary experiments was added to the semiconducting layer at various concentrations from 0 to 5% on disc specimens. These specimens were then subjected to A. C. dielectric breakdown tests. The analysis of the Weibull distributions of the breakdown strengths revealed that these breakdown strengths were considerably improved at concentrations from 3 to 5 %. In particular, the 10% Weibull breakdown strength was improved by 50%. Furthermore, the insulation of the specimens were subjected to physical and chemical analyses. It was found that a layer diffused with the additive is formed in the insulation in close proportion to the concentration of the additive, and that the density of the amorphous portion in the insulation increases with its formation.